16-Civ-A3 Elementary Environmental Engineering · December 2018
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
Paper format. National Exams, December 2018 — 16-Civ-A3 Elementary Environmental Engineering. Three hours; closed book with one candidate-prepared 8½ × 11 double-sided aid sheet; approved Casio or Sharp calculator only. Seven problems are printed, each worth 20 marks, and any five constitute a complete paper (maximum 100 marks). All seven are solved here, because the set is intended as a study resource rather than an exam script. Section marks are shown in brackets at the left margin of each question and are reproduced from the final-page Marking Scheme.
Reference texts.
Question text not reproduced: the examination questions are © Engineers and Geoscientists BC. Open the official past paper (linked at the top of this page) to read the question, then follow the worked solution below.
Each unit targets a specific contaminant class, so that the barriers act in series (multi-barrier principle). Screening and grit removal takes out floatables and coarse solids that would foul downstream units. Coagulation–flocculation–sedimentation destabilises and aggregates colloidal particulates so they settle by gravity, and also removes a large fraction of natural organic matter and turbidity. Filtration (granular/dual-media) polishes the residual fine particles and provides a physical barrier to protozoan cysts. Disinfection (chlorine, UV or ozone) inactivates pathogenic microorganisms, sized on the C·t of the most resistant target organism; where dissolved inorganics (hardness, iron, manganese) or dissolved organics are significant, softening/oxidation or adsorption (activated carbon) is added ahead of filtration. The final clearwell provides disinfectant contact time and storage and carries a residual into distribution. This sequence converts a raw surface water into potable water meeting the GCDWQ.
The three main processes are the biological nutrient-removal zones. In the anaerobic zone, phosphate-accumulating organisms release phosphorus and store carbon, the precondition for enhanced biological phosphorus removal. In the anoxic zone, heterotrophs use nitrate (recycled from the aerobic zone) as the electron acceptor, converting it to nitrogen gas (denitrification). In the aerobic zone, nitrifiers oxidise ammonia to nitrate and the phosphate-accumulating organisms take up phosphorus in excess (luxury uptake), which is then removed with the wasted sludge in the secondary clarifier. Together they cut both nitrogen and phosphorus well below conventional secondary levels.
Two non-technical principles for lifetime compliance: (1) Operator training, competency and adaptive management — BNR performance depends on skilled operation (controlling sludge age, recycle ratios and dissolved oxygen), so a certified-operator programme, standard operating procedures and continuous performance monitoring keep the plant within its permit as loads and seasons change. (2) Governance, funding and stakeholder accountability — sustained compliance requires a long-term asset-management and reinvestment plan (life-cycle funding for renewal), transparent regulatory reporting, and public/stakeholder engagement so that the community supports the rates needed to operate and upgrade the facility over its life. These non-technical measures are what keep a technically capable plant actually compliant decade after decade.
